| Occurrence of trace antibiotics in the environment has received a growing international concern. Wastewater treatment plants (WWTPs) were considered to be one of the main sources for the antibiotics occurrence. In this study, occurrence and fate of the trace antibiotics in wastewater were investigated, and meanwhile, the technologies for removing antibiotics in wastewater were explored to achieve the aim of reduction of antibiotics discharge from WWTPs, which would be beneficial to the healthy development of the ecological environment. Six antibiotics that had the highest using frequencies were selected as target pollutants, of which detection methods were established based on high performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS) technology and solid phase extraction (SPE) technology. Six WWTPs in Dalian were sampled and analyzed. Results demonstrated that the concentrations of the target antibiotics in WWTPs influents and effluents were in the range of20-711ng·L-1and29-728ng·L-1, respectively. During the wastewater treatment processes, two β-lactams, cefalexin and cefradine were well removed by biodegradation in the biological treatment stage (the average removal efficiencies were100%and72%, respectively), two fluoroquinolones, norfloxacin and ofloxacin were partially removed through physical adsorption by sludge (the average removal efficiencies were70%and40%, respectively), while two macrolides, roxithromycin and azithromycin showed negative removals in the wastewater. In addition, the concentrations of the target antibiotics were detected in the range of2-396ng·L-1at the surveyed coastal areas of the Yellow Sea.Technologies for removing trace antibiotics from the wastewater were studied subsequently. Membrane technologies and advanced oxidation processes were mainly studied. In the study of nanofiltration (NF) combined with ozone-based oxidation processes, results demonstrated that NFX membrane had effective rejections (>98%) for the four antibiotics, meanwhile, NF concentrate was efficiently disposed by UV/O3process with the removal efficiencies of antibiotics higher than94%, removal of dissolved organic carbon (DOC) achieving40%, the increase of biodegradability by4.6times and the reduction of ecotoxicity by58%.In the study of rejection of antibiotics using forward osmosis (FO), it was found that the added spacer over the membrane in the FO cell could enhance the rejections of antibiotics in wastewater. The rejection was increased by2.3-8.5%in different experiment conditions. The mechanism was supposed to be that turbulence produced due to the spacer in the channel disturbed the boundary layer on the membrane surface and urged the antibiotics diffusing from the layer into the bulk solution, which reduced the permeable pressure of antibiotics across the membrane and prevented the diffusion through the membrane. In addition, a novel forward osmosis process functionalized with electrochemical oxidation (FOwEO) was established by combining the electrochemical oxidation and forward osmosis filtration process. In the treatment of trace antibiotics from wastewater, it was found that compared with the traditional FO process, rejections of antibiotics were higher (maximumly45%) in FOwEO, while degradation efficiencies of the selected antibiotics were higher (maximumly30%) in EOwEO compared with those in the undivided electrolytic cell (EC). Coupling effects were obtained between the forward osmosis filtration and electrochemical oxidation in FOwEO. Moreover, the WWTP secondary effluent (concentrations of target antibiotics in the range of134-1311ng·L-1) were well treated by FOwEO, and antibiotics were detected below the limits of the method in both effluent and concentrate after the treatment. To sum up, rejection and degradation of antibiotics were achieved at the same time in FOwEO with the issue of FO concentrate disposal being solved. |
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